Well casing



P atente d June 25, 1946 UNITED STATES .PATE

NT OFFICE WELL CASING Edwin C. Wright, Beaver, Pa, assignor to National Tube Company, a. corporation of New Jersey No Drawing. Application March 25, 1043,

Serial No. 400,551

The pipe and tubing used as casing for shutting out water in the drilling of wells for the production of oil, and also water wells for irrigation purposes, has to resist high external pressures due to the occurrence of water-bearing strata at considerable elevations above the bottom of the hole.

The drilling of oil wells to depths as great as 15,000 ft. has greatly increased the stresses imposed upon casing, especially in such very deep oil wells; It has long been known that the resistance of the casing to external pressure is dependent entirely upon the true elastic limit of the casing material. As soon as the external pressure develops a stress in the casing which exceeds the true elastic limit of the material in the casing, the structure becomes unstable and collapses much like a very long column. As a result, the casing used in oil and water wells has had to develop a true elastic limit of higher and higher values as the depths of the wells increased.

At the present time the API lists four standard grades of casing which are classified according tothe yield point of the material. The yield pointis proportional tothe' true elastic limit of the 09s ing. These grades are tabulated below I Yield point Grade DJ'L r-zs. 25,000 Iii-40 40,000 1-55 55,000 N-80 The grade of casing employed of any given size is determined by the depth of the hole.

2 Claims. (01. 130-47) casing and oil well tubing is necessary for wells below 6,000 it. deep.

Studies of the physical properties and collapse resistance of thoroughly deoxidized high-phosphorus steels have shown me that adjustments of the carbon, manganese, and phosphorus contents enable theproduction of deep well casin and tubing which will be adequate for all existing wellsdrilled. The general composition of these high phosphorus steels, which must be made extremely low in oxygen combined with the iron, is tabulated below:

Carbon .15- .40 Manganese .30-2.00 Phosphorus .10- .30 26 Silicon .15- .50 Sulphur .05 max. Oxygen as FeO Under .02 Iron Balance -As typical examples of the properties of steels made in this range of composition, Table I shows the tensile strength, yield point, elongation in 2" (ductility) and Charpy impact properties of sev-,v

eral steels made with the high phosphorus content and thoroughly deoxidized as to contain less .35 than .02% oxygen as FeO.

Table I 1 Steel No.

out... 0. 20 0. a0 0. s1 0. a0 0. a0 0. 41 0. a0 Manganese l. 00 l. 25 1.48 1. 28 1.50 1. 53 l. 51 Bill .20 .20 .21 .2 .22 .21 .2: P1108 1101113"... .18 .11 .12 .21 .19 .12 .20 Sulp ill .0?! 031 .026 .021 029 .022 027 Tensile Emil 103, 560 99, 610 106, 880 109, 510 116, 880 121, 040 131, 040 Yield strengt 12,000 00 74,000 ,000 01,000 04,000 01,000 Elongation 2"--- 20.2 01.0 21.0 20.2 20.4 22.0 20.0

Oharpy impact" 30. 1 37. 2 80. 2 20. 6 28. 1 24. 2 23. 0

The first two types of casing-namely, F-25 and HAD-are produced readily from regular open hearth steel or simple analysis, at least The physical properties given in Table I for the seven dlflerent typical compositions show that pipe and tubing of satisfactory ductility, toughness and yield point can be produced from these 4 I claim 1. Well casing made of steel containing from .15 to .40% carbon, from .30 to 2.00% manganese,

from .10 to 30% phosphorus, from .15 to 50%- 5 silicon, not more than .05% sulphur, less than .02% oxygen combined with iron and with the remainder substantially all iron.

2. Well casing made of steel containing sutflcient phosphorus to materially enhance the col- 1o lapse resistance of the casing and less than .02%

- oxygen combined with its iron.

EDWIN C. WRIGHT. 

